I've performed some tests with 2.3.2 beta release and in general it
works better, slapd stays alive, but it still takes about 200 MB of
memory and it does NOT free it after the loading.

That is normal; you can reduce the entry cachesize in slapd.conf if you
want it to keep less memory.

Also the log files are still not removed after the checkpoints, this
is also the case when doing manual checkpoint and "db_archive -d".
There are 104 log files in DB_HOME directory, each of 10MB. The only
way to clear the logs is to shutdown the server.

What else I should check? I've run out of ideas to solve this
problem.

You need an additional patch to BerkeleyDB and to back-bdb. The
BerkeleyDB patch is here